Cellulose is a beta 1–4 linked polysaccharide and the principal component of cotton, which is a well-known material for the production of fabrics and in very widespread use. Cellulose is capable of cross-linking by hydrogen bonds which form between the cellulose chains.
The majority of garments purchased world-wide contain at least some cellulose fibres in the form of cotton or rayon and these suffer from the well-known problem that on exposure to water, such as during domestic laundering, fibre dimensions change and cause shrinking, shape change and wrinkling of the garments. It is believed that this is due to release and reformation of hydrogen bonds.
So-called ‘durable press’ treatments of fabrics are intended to overcome these difficulties. One of the most common methods of durable pressing uses a crosslinking agent to immobilise cellulose at a molecular level. Known cross-linking agents for whole cloth include formaldehyde, and urea-glyoxal resins. Other proposals include epichlorohydrins, vinyl sulphones, acrylo-amide and acrylo-acrylates. None of these proposed technologies have demonstrated any commercial viability for domestic on finished garments use to date.
A range of industrial processes for use in the manufacture of finished fabrics are known.
U.S. Pat. No. 4,588,761 discloses poly-urethane coating compositions for use with a transfer paper or other temporary support. These comprise an isocyanate which is preferably blocked. This is an industrial treatment process for fabric and is inherently unsuitable for use at home on finished garments.
JP 53035098 discloses a finishing process for treating woven or knitted cellulosic fabrics with a processing solution comprising a urethane prepolymer with blocked terminal isocyanate groups, a gloxal-amide type cross-linking agent and a bromo-fluorinated metal. The process is not suitable for domestic application to finished garments.
JP6346374 discloses finishing of fabric or a sewed product by a stepwise industrial process comprising treatment with a blocked isocyanate, heat treatment and subsequent use of a gas phase cross-linking agent. A similar process is disclosed in JP8127972.
JP 55093882 discloses a method for flocked fabric production which uses masked isocyanate. JP 9316781 discloses a finishing agent for use in the production of yarn, paper or films which comprises a blocked isocyanate. JP 11131374 discloses an industrial process for the product of water repellent fabric by treatment with a glyoxal-based resin crosslinking agent, an organo-fluorine compound and a isocyanate based cross-linking agent. Followed by heat treatment for 0.5–5 min. A similar process is disclosed in JP 2000129573.
An alternative proposal is to use poly-acids such as BTCA (butyl tetra carboxylic acid) or citric acid as crosslinking agents. These can esterify with the —OH groups of the cellulose to form a covalent cross-link. The covalent cross-link is not disrupted by water and this both prevents deformation of fabrics and assists return to a flat state. One of the difficulties with this approach is that a sodium hypophosphite catalyst is generally used to cause the esterification reaction to proceed and the treated articles require heat curing. Moreover, these poly-acid materials are highly water soluble and are difficult to deposit on fabrics.
A preferred durable press system suitable for domestic use should be a non-toxic, one component, catalyst-free system with low iron-cure times, have some affinity for the fabric surface and not cause fabric strength losses. It should also avoid the need for specialised equipment and the use of use of difficult materials such as vapour-phase formaldehyde.